This invention relates generally to sputtering apparatus, and more particularly the invention relates to a circular magnetron sputtering apparatus.
Ion plasma sputtering and ion beam sputtering are the two predominant procedures for ion sputtering. In ion plasma sputtering a gas discharge plasma is produced directly at the sputtering surface, and the ions produced in the plasma bombard a target which is at a large negative potential. The most widely used method for deposition of films, owing to its simplicity, is the ion plasma sputtering method. However, conventional ion plasma sputtering techniques are hindered by low rates of sputtering, high working voltages, intense temperatures, and radiation defects in the deposited film.
Attempts at eliminating these limitations of the ion plasma sputtering have led to the creation of better sputtering systems with high deposition rates. The most important development has been the magnetron system for ion sputtering of material as discussed by Danillin and Sirchin in "Magnetron Systems for Ion Sputtering of Materials" Moscow Institute of Electronic Engineering, No. 4, pgs. 7-18, July-August, 1978 (translation copyrighted by Plenum Publishing Corporation 1979), and Chapin, "The Planar Magnetron: A New High Rate Sputtering Source," Vacuum Technology Associates Inc. As discussed by Danalin and Sirchin, the magnetron ion sputtering system is similar to the microwave magnetron device in using crossed magnetic and electric fields. However, the magnetron ion sputtering device is a diode type sputtering system in which the atom of the sputtered material is removed from the surface of a target as it is bombarded with ions of the working gas, usually argon, produced in an anomalous glow discharge plasma. The principal elements of the system are a target cathode, an anode, and a magnetic system. A characteristic feature of the system is the presence of a magnetic field at the sputtered surface of the target which makes it possible to localize the plasma of the anomalous glow discharge directly at the target. When a dc voltage is applied between the target (negtive potential) and the anode (positive or ground potential), an inhomogeneous electric field is produced and an anomalous glow discharge is developed. The electrons emitted from the cathode under the influence of the ion bombardment are captured by the magnetic field and remain as if in a trap produced by the magnetic field, which returns the electrons to the cathode, and by the target surface which repels the electrons. The electrons remain in this trap until several ionizing collisions take place with the atoms of the working gas as a result of which the electrons loose the energy acquired from the electric field. Before the electron falls on the cathode, the greater part of its energy is used for ionization and excitation of the gas thereby considerably increasing the activeness of the ionization process and leading to an increase in the concentration of the positive ions at the target surface. This in turn leads to an increase in the intensity of the ion bombardment of the target and to a considerable increase in the sputtering rate.
U.S. Pat. No. 4,434,042 discloses a planar magnetron sputtering apparatus which has proved commercially successful in producing planar sputtered films with an improved uniformity. However, a need exists for fabricating coated fibers and rods of semiconductors and superconductors. However, known magnetron sputtering apparatus are limited in use to fabricating planar thin films of superconducting material and other material. Conventional methods for coating thin films on rods, tubes or fibers consist of sputtering from a source designed to deposit on a planar or flat surface. In order to obtain uniform coatings all around the substrate, the substrate must be rotated or otherwise turned during the sputtering procedure. In coating by evaporation the same situation exists because the evaporated coatings are produced under high vacuum conditions, and the materials are deposited in a line-of-sight fashion.